High Surface Area of Porous Silicon Drives Desorption of Intact Molecules

• Published in: Journal of the American Society for Mass Spectrometry 2007-11, Vol.18 (11), p.1945-1949
• Main Authors: Northen, Trent R., Woo, Hin-Koon, Northen, Michael T., Nordström, Anders, Uritboonthail, Winnie, Turner, Kimberly L., Siuzdak, Gary
• Format: Article
• Language: English
• Subjects: Desorption; Exact sciences and technology; Instruments, apparatus, components and techniques common to several branches of physics and astronomy; Ionization; Ions; Lasers; Mass spectrometers and related techniques; Mass spectrometry; Microscopy, Electron, Scanning; Molecular structure; Nanotechnology; Nanowires; Physics; Porosity; Porous silicon; Silicon; Silicon - chemistry; Silicon substrates; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Surface area; Surface energy; Surface Properties; Surface structure
• ISSN: 1044-0305; 1879-1123; 1879-1123
• DOI: 10.1016/j.jasms.2007.08.009

The surface structure of porous silicon used in desorption/ionization on porous silicon (DIOS) mass analysis is known to play a primary role in the desorption/ionization (D/I) process. In this study, mass spectrometry and scanning electron microscopy (SEM) are used to examine the correlation between intact ion generation with surface ablation and surface morphology. The DIOS process is found to be highly laser energy dependent and correlates directly with the appearance of surface ions (Si n + and OSiH +). A threshold laser energy for DIOS is observed (10 mJ/cm 2), which supports that DIOS is driven by surface restructuring and is not a strictly thermal process. In addition, three DIOS regimes are observed that correspond to surface restructuring and melting. These results suggest that higher surface area silicon substrates may enhance DIOS performance. A recent example that fits into this mechanism is the surface of silicon nanowires, which has a high surface energy and concomitantly requires lower laser energy for analyte desorption.